Electric switch.



no. 696,969. Patented Apr. 8, m2. E. M. HEWLETT.

ELECTRIC SWITCH.

(Application filed Aug. 18, 1901.]

(No Model.)

9 m OW m t 1 w a a 2 v 9 f m n WLtnesses.

, Edward MHewLett. 9

Atty.

UNITED STATES PATENT OEEIcE.

EDIVARD M. IIEIVLETT, OF SOIIENEOTADY, NEIV YORK, ASSIGNOR TO GENERALELECTRIC COMPANY, A CORPORATION OENEVV YORK.

ELECTRIC SWITCH.

SPECIFICATION forming part of Letters Patent No. 696,969, dated April 8,1902.

Application filed August 16, 1901. Serial No. 72,235. (No model.)

To all whom it may concern.-

Beit known that I, EDWARD M. I-Inwnnrna citizen of the United States,residing at Schenectady, in the county of Schenectady, State of NewYork, have invented certain new and useful Improvements in ElectricSwitches, (Case No. 1,851,) of which the following is a specification.

In starting up electric motors considerable annoyance is often createdby tripping of the circuit-breaker by the first rush of current when thecircuit is closed. Motors are very often used without rheostats forgraduating the starting-current, and in such cases the first closure ofthe switch permits a large volume of current to flow through thearmature much in excess of that which the motor normally draws, and as aresult the circuitbreaker which is calibrated for an ordinary overloadis tripped when it is unnecessary. The armature of the motor willusually stand a heavy current for a very short period, such as isoccupied in the motor climbing up to its normal speed, and it istherefore desirable to prevent the tripping of the circuit-breaker whileclosing the switch. My invention involves means for accomplishing thisresult and comprises, essentially, means of any character by which thecircuit-breaker is rendered less sensitive while the switch is beingshifted from its first position of contact to its fullclosed position.

I am of course aware that rheostats are frequently employed in startingelectric motors; but my invention relates more particularly to simpleswitches in which there is no graduation of the circuit resistance.

The best means I have yet devised for carrying out the inventioncomprises a mechanical device operated by the movement of theswitch-blade by which the calibrating-spring of the circuit-breaker isput under increased tension for a short period after the circuit isfirst closed by the switch, and then a reduction of tension is effected.By this means the heavy current passing at the first instant of closureof the circuit is unable to overcome the tension of thecalibrating-spring and cannot therefore trip the circuit-breaker; butafter the motor has acquired its normal work ing speed the tension isrelaxed, permitting it to respond to the designed overload for which thecircuit-breaker was set or callbrated. Various means for efiecting thisresult will occur to those skilled in the art; but the particular meansI employ comprises a cam actuated by the switch by which a leverconnected with the calibrating-spring is shifted to increase the tensionof the spring at the moment when the switch-blade enters the clip, andthen after the movement has progressed sufficiently to permit the motorto acquire speed a slope on the cam permits a relaxation of the springtension. I desire to have it understood, however, that many othermechanical devices for effecting an increased tension and subsequentrelaxation of the spring or of otherwise decreasing the sensitiveness ofthe circuit breaker until the switch is fully closed are within thescope of my invention.

My invention therefore comprises a motorstarting switch and connectionstherewith by which the sensitiveness of the circuit-breaker is reducedfor a short period during circuitclosure. In a more specific sense itcomprises a switch provided with connections for putting increasedtension on the calibratingspring of the circuit-breaker during circuitclosure.

Other features of novelty will be more particularly hereinafterdescribed and will be definitely indicated in the claims appended to thespecification.

In the accompanying drawings, which illustrate the invention, Figure lis a side elevation of a motor-switch and circuit-breaker embodying myimprovements. Fig. 2 is a partial view of the tripping device of thecircuit-breaker on a plane at right angles to that of Fig. 1. Fig. 3 isan elevation of the switch on a plane at right angles to that of Fig. 1.

1 represents a supporting board of insulating material, preferably slateor some other fireproof insulating material as commonly employed indevices of this kind, in the upper part of which is mounted a trip-coil2, a setting-handle 3, a trip-armature 4, a calibrating-spring 5, and anadjusting device 5 therefor. These parts are of: known construction,representing a well-known type of circuit-breaker, and do not requirefurther description.

6 represents the blow-out chute, the circuitbreaker shown in thedrawings being of a magnetic blow-out type for extinguishing the arc ofcircuit rupture.

7 7 represent the circuit-terminals, and 8 a bridging-contact commonlyemployed to 40 close the main circuit. 1

9 represents a switch-clip of the ordinary type, except that it islonger than those commonly employed, and 10 a knife-blade switchleveradapted to enter between the elastic jaws of the clip to efiect goodcontact.

It will be understood by those familiar with the art without furtherdescription or illustration that the switch is employed to close acircuit including a counter-electromotiveforce translating device-as,for example, an electric motor-through the circuit-breaker and that thelatter is calibrated, by special adjustment of the spring 5, to open thecircuit upon a definite overload. In starting up the motor, however,there is a great rush of current through its armature, since thearmature has at the instant of starting no counter electromotive force,and this is sufficient to trip the circuit-breaker if the latter is setto respond to a moderate overload. This of course creates greatannoyance, as the circuit-breaker must be held down in some way untilthe motor is at speed. I effect the result automatically by anattachment to the switch which renders the circuit-breaker lesssensitive immediately after circuit-closure. One mode of eitecting thiscomprises a cam 11, secured to the switchblade at its axis, cooperatingwith a lever upon which is mounted a roller bearing on the periphery ofthe cam. The free end of the lever connects with arod13,whiohisconnected at its upper end to a lever, through which passes freely therod 14, upon which the adjusting-nut 5 is mounted. The cam is set withrelation to the axis of the switchlever, so that when the latter firstengages the clip the roller 12 will bear upon the highest point of thecam, which adds to-the tension of the spring, and of course renders thecircuit-breaker less sensitive. Progressive movement of the switch-levertoward the board then gradually relaxes the tension of the spring bypermitting the roller 12 to roll down an incline on the cam, so thatwhen the switch is fully closed, as indicated in Fig. 1, the extratension is fully relaxed and the circuit-breaker will be responsive tothe overload for which it is normally set. In order to permit theseresults, the switch-clip is lengthened so as to give a considerablerange of movement during contact with the switchblade.

Having thustdescribed my invention, what I claim as new, and desire tosecure by Letters 'Patent of the United States, is

1. The combination with a motor-starting switch, of an automaticcircuit-breaker in circuit therewith, and connections with the switchfor temporarily raising the trippingpoint of the circuit-breaker whenthe circuit is first closed. I

2. The combination with a switch, of an automatic circuit-breaker incircuit therewith, and connections for temporarily increasing thetension of a calibrating-spring when the circuit is first closed. 3. Thecombination with a switch, of an automatic circuit-breaker in circuittherewith, and connections for temporarily increasing the retractileforce of the tripping-armature when the circuit is first closed.

4. The combination with a switch, of an automatic circuit-breaker incircuit therewith, and mechanical connections between the switch andcalibrating-spring of the circuitbreaker for temporarily increasing thetension, of the latter during circuit-closure.

In witness whereof I have hereunto set my hand this 14th day of August,1901.

EDWARD M. HEWLETT.

Witnesses:

BENJAMIN B. HULL, MARGARET E. WOOLLEY.

